This invention relates to high density random access data storage, and is more especially directed to an optical memory system in which laser light is employed to write and read data via two-photon processes within an irradiated volume which can be controllably displaced in three dimensions. A key feature of this optical memory is the use of a light-sensitive protein called bacteriorhodopsin. This protein is capable of being oriented and can emit an electric signal indicative of the binary state of an irradiated volume.
A number of attempts have been made to produce optical memories that employ non-linear optical processes. U.S. Pat. No. 4,458,345 describes a two-photon process within an irradiated volume that exposes a sensitized medium. The medium is a four-level material, and the two-photon process generates a microscopic interference pattern. The gating property of the two-photon photochemistry provides for nondestructive reading. Patterns can be produced at several depths below the surface, and thus a three-dimensional capability is possible.
Another two-photon three-dimensional memory has been proposed based on the use of two distinct photochemical forms of spirobenzopyran. In this approach, the storage medium is an unoriented organic chromophore in a polymer matrix. The writing process involves a two-photon induced photochemical change involving heterolytic cleavage, the read process is based on the observation of fluorescence from the merocyanine form, and there are blurring effects from the two-photon induced photochemistry that occurs in adjacent bit cells outside of the irradiated volume.